Nonetheless, a recent case of BO/OP in a boy LY3009104 was associated with a severe immune reaction to Mycoplasma pneumoniae infection [24]. The cryptogenic (undefined aetiology or idiopathic presentations of OP) actually the most relevant form of OP (also called primary OP or COP) [10�C12, 31] is excluded in this work for comparative purposes.Typical fibrinous or fibrinosuppurative pneumonias in feedlot cattle are characterised by accumulation of exudates in the alveolar spaces and bronchioles. Organization of this material is one of the most conspicuous images of the pneumonic lesion in calves, which died during severe M. haemolytica pneumonia [9]. Organising exudates consist of whorls of fibrin admixed with streaming neutrophils (oat cells) inside alveoli and bronchioles [32].
As has been noted, resolution of the lesions in severe cases is incomplete and evolves toward organisation from fibrinous to fibrous plugs covered by type II pneumocytes [26] (Figures 1(a), 1(c), and 1(d)). Experimentally, this change has been seen by 15 days post inoculation and beyond in a model of progression of lung lesions referred in sheep [6]. Therefore, lesions described in BO/OP due to bacterial infections, such as Streptococcus pneumoniae, Mycoplasma pneumoniae, Legionella pneumophila, and Pseudomonas aeruginosa [9�C12], are similar to those observed in chronic cases of exudative pneumonias (fibrinosuppurative bronchopneumonias) in feedlot cattle. The lobar distribution of BO/OP [10�C12] is also in accordance with the pneumonic lesions found in shipping fever [9].
It was postulated that development of BO/OP lesions induced in mice is the result of the severity of initial lung injury inciting an augmented expression of proinflammatory and profibrotic cytokines [33]. This condition is likely to occur in severe cases of shipping fever pneumonia, considering the concomitant role of M. bovis and continuous exposure to environmental pollutants in the feedlot, which contribute to/or sustain the inflammatory response with progression to fibroplasia [1, 22, 34, 35].It is worth to mention that recently the chronic lung lesions recognized in pigs naturally infected with porcine circovirus 2 (disease named chronic postweaning multisystemic wasting syndrome [PMWS]) showed similarities with BO/OP [36].4.
Bronchiolar Involvement as a Result of Large Airway DiseaseArising Brefeldin_A from virus-induced bronchiolar insult, air pollution and lipopolysaccharide (LPS) may also instigate the severity and permanence of chronic inflammation with or without bacterial superinfection. For instance, higher morbidity and more severe cases of RSV occur in infants living in zones with high levels of air pollution [18�C20]. Correspondingly, the highest morbidity and mortality related to respiratory viral infections occur in younger calves entering the feedlot pen [1].